Strain-balanced superlattices for radiation-hard solar cells in extreme conditions

In my proposed research, I aim to improve the performance and longevity of inverted metamorphic (IMM) multi-junction solar cells operating in extreme space environments. Solar cells used in space undergo damage from high-energy protons and electrons in the earth's Van Allen belts and on the moon where there is no protective magnetic field. Space photovoltaics often simultaneously face low temperatures, such as in partially shaded regions of the lunar poles and regions with low light intensity. InGaAs alloys are typically used as the bottom subcell of IMM cells but exhibit poor radiation hardness, limiting IMM cell performance at end-of-life (EOL). My research aims to improve the radiation hardness of bottom subcells by inserting novel strain-balanced superlattices with alternating layers of InGaAs and InGaP in the absorption regions of solar cells. InP and alloys containing In-P bonds exhibit exceptional radiation hardness owing to their ability to self-heal certain crystal defects at room temperature. My cell designs will combine thin phosphide layers to facilitate material repair with thin InGaAs layers for near-infrared light absorption. Devices will be tested at temperatures as low as 83 K to optimize for a variety of space environments. I will benchmark my superlattice solar cells against conventional 1 eV InGaAs, AlInGaAs, and InGaAsP solar cells. After ensuring excellent beginning-of-life performance, I will irradiate my best cells with high-energy electrons and conduct further device testing. By the fellowship's end, I will pinpoint the most radiation-hard bottom subcell through cyclical optimization of material quality and device structures. My proposed research could improve EOL efficiency of IMM solar cells operating in extreme space environments. Furthermore, my results could directly apply to radiation hardening of InGaAs laser power converters used in permanently shaded regions of the moon for ice mining operations and superlattice structures used in GaAs middle subcells.

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